Pneumatically actuated brake slack adjuster



May 22, 1951 A. F. SHIELDS 2,554,065

PNEUMATICALLY ACTUATED BRAKE SLACK ADJUSTER Filed Nov. 1, 1947 2 Sheet's-Sheet 1 IN VEN TOR.

ALBERT F. SHIELDS ATTORNEY y 1951 A. F. SHIELDS 65 PNEUMATICALLY ACTUATED BRAKE SLACK ADJUSTER Filed Nov. 1', 1947 2 Sheets-Sheet 2 ATTORNEY Patented May 22, 1951 OFF/ICE.

. PNEUMA'lICALLY ACTUATED BRAKE ,--,SI4AQK ADJUSTER,

Albert F. ShildsfFor'est Hills, Y., 'assignor to S ier-Bath Gear 8g Pump 00., ,Inc.,- North Bergen",'"Ni'J.,a (reiteration of New 'Jersey Application i iotifiter 1, 1947, Serial No. 783,585

The invention relates ingeneral to an automatic slack adjuster for; fluid" pressure brakes and particularly relates to adjusting mechanism for use on; automatic'vehicle brakes inwhich slack in the brake operatingmechanismisauto matically adjusted in response to the.;usual brake mechanism when the control therefore moves beyond its predetermined range of norni'alLoperation.

The present disclosure constitutes another embodiment of the invention disclosed in my copending application Serial No." -760;416, filed July 11 1941 l, H

As recited "in the-prior,application-it has been known inthis art-=to incorporate a 'slackad= justeror wear compensatingmechmisinin and as part of theusual -brake--applyingmechanism so that an over-travel-f"suchmechanism'in its normal opera-tionwil-l re-adjust the brakeapplying mechanism insuch way as will-compen sate automatically for wearin the operative' 'el; ments of the brake applying mechanism-k These known-deviceshave not--proven-entirely satisfactory in actual service particularly when installed on automotive vehicles, among other reasons mainly, because they were unsafew The parts thereof which form-the :wear "compensating means is an integral -part'of the -brake applying mechanism and thusaaa failure invtheir automatic slack adjuster feature would mean a complete brake failure: Furtherszin theseaknown-devices the automatic adjuster elements are quite apt to function accidentally due to theirzinterlocking features; tomake, =or;;at-, leastattempt to: make, an; adjustment when. not needed; ielementsxawere often .used which could notwwithstandnthe vibra-' tion and rough .usage to which normal "operation" wouldfsubject them and general such .devices are so complieateqin structure and operation :as.

to render their use too expensive and in many cases not; 1 entirely; suited nfor heir intended purpose.

- This invention {as 1 we H v closed in the prior application-is. 0 provide a simple form of slack adjuster @whichds supple-:

nta to d 1 11 e rn barrc a d dras n add brake actuating mechanism, otherwise: complete moved from any possibility of partaking in the usual braking operation and which will come into the invention dis-.1

I 18 Claims. (0]. 1887795,). 2'

operation only when the power generating element of the-conventionalbrake applying mechanism moves over an excessive range of travel in -its-efiect to cause the desired'clutchin'g action of=thebrakes.- a 1i @1 :the prior application the re-setting of the cam relative to the brake shoes controlled thereby was by-mechanica1 meanswh-ile in this-application. device the same objectives-are attained by pneumatically powered means, valvular controlled by any excessive travel of the pneumati= cally actuated brake applying mechanism. 1

-Various. other objects and-advantages of the invention will be inpart'obvious' from a'con sideration of the methodfeatures of the disclosure "and from an inspection'of the accom panying drawing and in part will be more'fully set: forth-inthe following particulardescription of oiiemethod-of practicing theinvention; and the inventionalso-consists in -certain new and novel modifications of the preferred method and of other features of construction and combination of parts; hereinafter set forth and claimed.

- In the accompanying drawings:-

A Fig. 1 is a view =partl-y 'in' vertical "transverse section of awheel brake drum, associated shoes and their operating cam, and partly inelevation showing an attachment theretoconstituting a preferred embodiment of the invention and the partsin section taken on the broken line ll ofFig.2;'..-.

Fig. 2 is an enlarged view mainly in side elevation of the device shown in-Fig. 1;

. Fig. Sis an enlargedviewppartlyin si'de'elevation and with parts broken away and partly in section of the brake'actuating device shown in .thepreceding figures; 1 1 "Fig. '4 is.a longitudinalfsectionalview taken on-..thel horizontal plane indicatedby the line 4 4. of. Fig. 3with the movable parts of both Figs. 3 and 4,:shovvn in their normal inopera tive,non-braking position} Fig. 5 is an axial sectional view of the cam adjuster" taken on the line 5'5 of Fig. 3 and separated from its mounting;

iFiggifi is a detailed transversesectional view takenjon" th'e'lin'e" 6-'-6"of Fig"; 5 looking upwardly as indicated by the arrows, and

i i7. is j a detailed section taken on the line l llof Fig.4. f

In' the drawings and tionallvehicle wheel-brake parts there-is illustratedlimEigsi l and:-2 aneaxle housing *A containing a wheel driving axle B for turning wheel C and associated brake drum D. Mounted within referring first to conventhe drum is a pair of distensible brake shoes E with an actuating double lobe cam F operating between their free ends and which free ends are held in engagement with the opposite long sides of the cam by a spring G. The cam is actuated by a cam shaft H mounted in bearing I in the form of a boss J projecting from a rear face plate K carried by the axle housing A and closing the rear side of the drum D all as is used with a known type of vehicle wheel-brake.

Referring first to the mechanism which operates the cam F to distend the shoes E and thus cause the brake to function, there is disclosed a source of pneumatic power and in this particular case the device as a whole is shown to be of the compressed air actuated wheel-brake type. The power for operating the brake is supplied to a two-part pressure containing casing Ill secured to the axle housing and between which two parts is clamped a freely swinging diaphragm l l. Compressed air is admitted conventionally to one side of the diaphragm through a tapped inlet I2.

A long main cam operating plunger 13 is slidably mounted in suitable bearing provided therefore in the casing 10 for reciprocating movement and at its inner end the plunger has a broad disklike head [4 secured to and movable with the central portion of the diaphragm. In normal operation the diaphragm has a relatively short amplitude of swing at its center, say of sufficient extent to move the head l4 from the solid line position to the dotted line position of Fig. 4.

The plunger l3 extends through the side of the casing l nearest the cam shaft and has this end threaded in the portion thereof which extends exteriorly of the casing. A clevis forming fork I5 is in adjustable threaded engagement with the projecting portion of the plunger as best shown in Fig. 4. An accordion l6 fitted to the casing and plunger defeats entrance of water or dirt to the interior of the casing through the opening in which the plunger slides. An operating arm ll is provided with an enlarged head I8 considered for the moment as secured to the cam shaft H to rock the same. A reduced end 19 of the arm has its free end fitted between the bifurcations of the fork I5 and is pivoted thereto by pivot pin 20. Up to this point the disclosure corresponds exactly to the similar parts in my above-identified application.

For the purpose of indexing the cam adjusting mechanism herein featured there is disclosed at the casing II] a valvular casing 22 of cylindrical form having its inner end fitted to the casing l0 and secured thereto through outstanding flanges 23 and screws 24 as best shown in Fig. 3.

The cylinder casing 22 is provided with a bore 25, see Fig. 4, extending entirely therethrough and closed at its outer end by a screwcap 26. The casing 22 is provided adjacent its inner end with a pressure intake port defined by an outstanding nipple 21 shown in full lines in Figs. 2, 3 and 7 and in dotted lines in Fig. 4.

Air pressure for operating both the cam F in the normal operation of the brake and for operating the adjusting mechanism herein featured 1s supplled from an external source indicated symbolically by the Y-coupling 28. One flexible tube 29 leads from the Y-coupling to the inlet I 2 and another flexible tube 30 leads from the p g to the pressure intake nipple 21 of the casing 22.

The cylinder casing 22 is also provided with a pressure outlet port defined by a nipple .1 see Figs. 4 and 7) to which is secured one end of a flexible tube 32, the other end of which leads to apparatus generally designated as a cam adjuster 33 which is secured to the head [8 as hereinafter described. Communication between the port defining nipples 21 and 3| is controlled by a plunger-type of valve 34 slidably mounted for axial movement in the bore 25 of the basing 22. The valve 34 is provided at one end with a plunger 35 guided in the inner end of the bore 25, projects therefrom into the casing l0 and is disposed in the path of movement of the plunger head [4 as it moves on its brake applying stroke. The plunger is normally spaced from and is thus completely independent of the normal amplitude of swing of the head [4, except in those cases where an excessive movement of the head I4 causes it to bear on and thus shift the plunger as a whole to the left of the showing in Fig. 4. The valve plunger 3435 is backed by a strong return spring 36 housed in the recessed barrel forming the outer end of the valve and bears at one end on the valve and at its other end on the cap 26 in a tendency to close the inlet supplied from the pressure source through tube 30. A pin and slot form of stop 59 limits the advance of the plunger valve 34 under pressure from, the spring 36.

In the region of the nipples 2'|-3l the valve 34 is reduced to form a waist-like portion defining an annular passageway 31. The portion of the wall of the bore 25 in which the passageway reciprocates is recessed to provide three parallel channels facing the passageway 31. Th innermost channel 38 is normally open to the in terior of the casing I0 through a bleeder vent 33. The outermost channel 40 is open to the port formed by the nipple 21 and thus to the source of pneumatic power supplied through the c0upling 28. The middle channel 4| is open to the port defined by the nipple 31 and thus to the adjuster 33 as shown in Figs. 3 and 4 to actuate the same.

The shoulders on the unreduced portion of the valve 34 defining opposite ends of the annular. passageway 31 are so related that normally, that is when the valve is in the position shown in Fig. 4, the left pressure intake channel 40 is closed, and both the bleeder vent 39 and nipple 3| lead-' ing to the cam adjuster 33 is open, but of course inactive.

When the valve 34 is shifted to the left of the showing in Fig. 4 as hereinafter described, the solid plunger end 35 of the valve 34 will be in position to close the bleeder vent 39, and the shoulder which defines the barrel portion of the valve in which the spring 36 is contained will un cover passageway 40 and thus open the supply of air pressure from the tube 30 through the nipple 21, passageway 31, channel 4| and nipple 3! to the tube 32 to actuate the cam adjuster 33.

Referring to the cam adjuster 33 reference is made particularly to Figs. 3 and 5 where it is seen that pressure from the tube 32 is caused to operate through a metering device to make a rotative adjustment of the cam shaft H. The metering device includes a cylinder 42 fitted to the head 18 and including flanges 43 fitted to,

and secured to the side of the head by screws 44 as shown in Fig. 3. The cylinder is provided with'a-bore 45 closed at one end by a head 46 and at its other end by a screw cap 41. A hollow piston 48 reciprocates in the bore 45 and is biased when. free of any pressure thereon to move and the carpi.

{parallel slots to; aim 1; "end of a worm jshait '5 52 is secured to the'shaft wi e pistn- 1 b nen o e ei h a t. leg of the pawl extendsfleng inner side'of the hollowfpistonand i the piston 48 is elevated towartls tfiejpos tion Opposite 'si'desfof t h with a lineofrack for i shown ,in Fig. 5 from any to ti illustrated to Whichit riiay h'ail'e pressure from the tube'tz. v a The upper leg 5!? of th'e p aiwl ex ds radially inwardly from the rack, all pos ions thereof overlaps the ratchet wheel 52 and isfprovided with an upturned end formin a springmaeutfment or spring stop 5'!. V A long, pawl actuating spring 58 reacts betweenj this stop and a fside bf the piston in a tenden'cy to keeplihe pa lrack and ratchet wheel teeth at all times interengaged as. shoWninFig. 30 Theshaft 5! isprovideg with wormss which meshes with a large worm: gear fifl splihedto the camshaft H as shown in ,In this Way any excessive travel of the diaphragm head L9, be

on below that beenffo'rced by '20 yond that necessary tb causetheno a1 ,appli 35 cation of the brake \VilI CELIE tlr'ie ind g methanism to reset the cam E in such away ES-.,wil1 cause it to take anyslachwhich ma devemp between the cam F the sht'je'sj sesame, brake drum D. The device is complete asth'e f 7 scribed. It has been roun n WW v installed on trucks, unsp'rung vehicles Sub ectd to high Vibration that there is; often tendency for the pawl teeth 55 to escapeir m their ere gagement with the teeth of ratchet wheel 52 With ratchet Wheel 52 thusflfreeto; airs/ momentarily therejis the possibility of ac,- cidental rotation of the shaft 51' and" thus a e? setting of the cam F relativeto' theibrakshoes E. In order to prevent any such p s 'bil't" "t i herein suggested thatdetent rneanslbepro v ed'to lock the ratchet wheel 52lat all'timesiagainst any unintended rotation For 7 this, urposes toothed cletent ee slidablynnounted on and. projects from a barrel 66' rema la lwith the cape! and centeredwithinthe spring 48 ,iii. the cylinder 42. The'detenttfl i qun eq with its toothed advance end in engagement with-the, teeth of'a' ratchet wheel 52and' nder lo; a a spring 52 housedwithin barr l, heart i one end on the 'detent andfat its otheriend a'ga t a'stopnut ts'screwedintofthe capfifl te'r. A pin and slotsto'p filtlimits' the perifiissi bl'e'lhovement of 'thedtlltf i,

In operation and assuming to be in their normal Jino'pe'ra't in the several figures, actuating M mittecl conventionally to the rightllside o diaphragm il when in'th e posfiti that "measured between; t r. p t ,v i the P1 5 willcause th'e mung-eras to act through fork 75 and aim I! to shift the. arm iIl Et clqckwise direction from its'normal position shown in Fig. 3 tor ra distance sufficient to act through the cam shaft H, and shift the cam F -from the position shown in Fig. 1 or adjusted variation therefrom lintosuch angled positionas will move the brake shoes. E outwardly into a braking engagement with .the brake drum as is usual in ,such cases. Releasing air pressure as by.re1eas ing-the foot pedal Whiclrcontrols the brake will permitor cause. the brake actuating mechanism to return to its normal, inoperative position by means forming no part of thisdisclosure of thebrakeactuating. mechanism Thelpowerfulreturn sprin 2-] islshown in Fig. 4,biased toreturn all parts to theirjnormal inoperative position. a l. Nowlet it he assumedthat in operating the mechanism to cause the brakevto function the head illl engages the exposed adjacent end of the plunger 35 to shift the valve 34 against there: sistance of its return spring 36 a distance to, cause the plunger 35 first to close the bleeder vent 39 and then to open communication between the source of pneumatic pressure admitted from pressure tube to channel 49 and throughpassageway 31, nipplefi! and tube 32 to the top of bore of cylinder 52-. The pressure thus admitted to the top of the cylinder as shown in Figs. 3 and 5 will depress piston 25 against the resistance of its return spring 49 thus placing spring 49 more .fully under tension-than it is normally. As the piston is thus lowered more or less, the teeth of the pawl 53 is slid idly past the teeth of the ratchet wheel 52 with some incidental compression of the pawl controlling spring 58. r The piston 48 isthus cocked ready to ,be elevated from such depressed position when freed of the depressing pneumatic power which forcednit downwardly in the cylin'fder 42. Spring 58 being at all times under load acts to maintain the teeth 55?. in a one-way lifting engagement with the teeth of ratchet wheel 52!. z Relieving the. mechanical pressure on the plunger by the retreat of the head it will perrnit spring-35 to restore the, valve 34 to its normal position as-shown inFig, 4;, This opens the cylinder 42 to relievelthe pressure therein back through tube .32, nipple 3l,,,channel H, passagee ways? and channel 33 to the bleed-ervvent 39 discharging into the casing, Ill. The piston 48 beineflthu s, relieved of itsair pressure. will per- Init .spring',,49 to react and elevate the piston back towards its normal position shown in Fig. 3,. .As the, piston-is thuselevated theteeth of pawl 5'3v e-engages the teeth of ratchet wheel 52 and: rotates the samelin a counter-clockwise direction, ,as indicated by thearrow in Fig. 5 to roe,

tate shaft BI and therethroughto cause worm,

59 and worm gear 69 to turn more or less and.

It isthus possible to operate ing mechanism automatically from a single source of pneumatic power. in turn controlled.

solely by the, usual foot pedal coinrnonly em moved o ac a he btekea Th brak la iustr, iri 'ifatur e a no ma l in eiiveandtb s ne use" I he of theljpneumatic phwernntil required toi' nalie the necessary resettingpi the brake appli'rine ar n then heln ce sar new r i .ap. ed, a tem iieal y and w thout ttenti n. on;

the part of the operator. When no longer needed v bat; the tea? applyingrnechanisrn as ,well as the brake adjust:

the supply of pneumatic power is automatically shut off from the brake adjuster.

I claim:

1. In a device of the class described, the combination with a shaft, a source of pneumatic power, a pressure chamber open to said source and provided with a swinging diaphragm having a normal amplitude of swing, a chain of mechanically connected parts between the diaphragm and the shaft to turn the shaft at each such normal amplitude of swing of the diaphragm, of pneumatically actuated mechanism independent of said chain of connected parts and controlled by an abnormally excessive amplitude of swing of the diaphragm for indexing the shaft, said mechanism including a valvular control having a plunger spring biased towards the diaphragm, disposed in the path of swing of the diaphragm, normally disposed in an inoperative position, spaced from the limit of normal amplitude of swing and engaged by and shifted by the diaphragm against the resistance of the spring when the diaphragm swings beyond said limit of normal amplitude of swing, and said pneumatically actuated mechanism comprising a chain of connected parts including indexing mechanism for moving the shaft over an arc of turn controlled by the extent to which the plunger is shifted be yond said limit of normal swing, said indexing mechanism including a ratchet wheel secured to the cam shaft, a pneumatically actuated piston,

a pawl carried by the piston for feeding the ratchet wheel and thus the cam shaft in one direction and said valvular control operatively controlled by the spring biased plunger to open the source of pneumatic pressure to the piston to move the same and thus actuate the ratchet wheel each time the diaphragm swings beyond said limit of normal amplitude of swing.

2. In a device of the class described, the combination of a shaft, an arm mounted to swing on the shaft and operatively connected as it swings to rotate the shaft, a worm gear drive carried by the arm to adjust the shaft rotatively relative to the arm, a source of power including a reciprocating member, a first chain of connected parts at all times connecting said reciprocating member with the arm to operate the same and a second chain of connected parts separate from and thus independent of said first chain and normally inoperative, said second chain including a pneumatic pressure system comprising a ratchet mechanism, a pressure conduit leading from a source of pneumatic pressure to said mechanism, and a spring loaded valve for controlling the same, said valve being normally closed and operatively connected to be opened to supply pressure from the source directly to said mechanism upon an excessive extent of travel of the reciprocating member and said valve normally operative to open the conduit to the outside of the device to bleed the ratchet mechanism, and said ratchet mechanism connected to the worm gear drive to cause it to adjust the shaft relative to the swinging arm on any such excessive travel of the reciprocating power member.

3. In a device of the class described, the combination with a mechanical element, a swinging diaphragm, a chain of mechanically connected parts between the diaphragm and element for causing the same to function when the diaphragm is actuated, and pedal controlled pneumatic means for actuating the diaphragm of mechanism for adjusting element incidental to an over travel of the diaphragm, said mechanism including a pneumatically actuated source of mechanical power and a chain of mechanically connected parts between said source and the element, a valve for controlling the supply of pneumatic pressure to said pneumatically actuated source of mechanical pressure, said valve being normally closed to intercept the flow of pneumatic pressure past the same and including a control disposed in the path of movement of the diaphragm when swinging beyond the point necessary to cause the first mentioned chain of parts to function thus to cause the last named chain or mechanically connected parts to function by reason of such over travel of the diaphragm and otherwise independent of the diaphragm.

4. In a brake slack adjuster, the combination of brake mechanism and a slack adjuster including a pneumatically actuated ratchet device operatively disposed to take up slack in said mechanism, a casing provided therein with a swinging diaphragm for operating the mechanism, a source of fluid pressure open to one side of the diaphragm to move the same on its operating stroke, a pneumatic conduit independent of any pressure in the casing and directly connecting the source with the ratchet device, a valve for controlling the conduit, said valve including a plunger disposed in the path of movement of the diaphragm and operatively associated with the same to cause the valve to open the conduit and thus place the ratchet device in communication with the source of fluid pressure upon excessive travel of the diaphragm, and a spring acting on the plunger for biasing said valve towards a normal closed position and opposing displacement thereof by the diaphragm.

5. In a device of the class described, the combination of a support, a worm shaft journaled in the support, an attachment to the support for locking the shaft against accidental rotation and for rotating the shaft by pneumatic power, said attachment including a pressure cylinder, a piston of cylindrical form slidably guided longitudinally in the cylinder and having its side pro vided with at least one longitudinally extending slot, an end of said shaft extending through the cylinder and through said slot and operative to prevent the piston from rotating, a ratchet wheel secured to the part of the shaft within the piston, a spring-loaded toothed detent at one end of the cylinder engaging the ratchet wheel and biased to resist its rotary movement and thus acting to lock the shaft against accidental rotation, a pawl housed within and extending lengthwise of the piston and provided with a line of saw teeth engaging the ratchet wheel to rotate the same on the working stroke of the piston, said pawl pivoted at one end to the piston and a spring engaging the other end of the pawl to maintain its teeth in engagement with the ratchet wheel in all positions of the piston, means for supplying pneumatic power to the cylinder to move the piston idly in one direction, and a spring acting on the piston to move it in its opposite direction on its working stroke.

6. In combination with a brake applying mechanism complete per se and comprising a chain of connected parts and a main motor including a diaphragm casing having therein a swinging diaphragm acting on the chain normally to operate said mechanism, of an attachment for readjusting the relation of certain parts of the chain to take up slack therein, said attachment including metering means acting on one of said parts and including a pneumatically actuated adjuster motor and. a conduit for leading pneumatic pressure from a source of supply to the adjuster motor, valvular means included in the conduit for regulating the pressure flow therethrough, said valvular means including a valve casing carried by the diaphragm casing, a valve slidably mounted in the valve casing, a valve spring acting normally on the valve to intercept flow from the source to the adjuster motor and to bleed the adjuster motor to the outside air, a plunger secured to the valve and having an end in the path of movement of the diaphragm, spaced from the diaphragm during its normal amplitude of swing and said diaphragm on an abnormal swing operating on the plunger to cause it to move the valve against the resistance of the valve spring into position to place the same in fluid connection with the adjuster motor to cause it to function.

'7. In combination with a brake system complete per se and including a mechanical brake, a pneumatic power device including a swinging diaphragm and a chain of connected parts between the diaphragm and the brake to function normally on a powered swing of the diaphragm in one direction, said diaphragm being limited in its amplitude of swing on its powered stroke by the movement of the brake into its final braking position, and which chain of parts is liable to develop a slack therein during use thus permitting an additional extent of amplitude of swing of the diaphragm on its working stroke before the brake functions, of an attachment to the system including normally inoperative pneumatically energized readjustment mechanism connected to the parts of the chain to take up the slack therein, said mechanism including a valvular control therefor disposed in the path of an abnormal swing of the diaphragm, a spring acting thereon and biased to move the control in the direction towards the diaphragm, a stop for limiting the movement of the valvular control towards the diaphragm, said valvular control when in engagement with said stop being spaced thereby beyond the normal amplitude of swing of the diaphragm and disposed to be engaged by the diaphragm and moved thereby against the resistance of its loading spring when the diaphragm develops an abnormal amplitude of swing to cause the valvular control to affect the readjustment 5o mechanism to function automatically as an incident of such an over-travel of the diaphragm.

8. The combination of a brake assembly including a mechanical brake, a pneumatically energized power unit formed of a main casing, a diaphragm dividing the casing into two separate parts, one part forming a pressure chamber and the other part a mechanism containing chamber, and a chain of connected parts including a plunger guided in the main casing and actuated by the diaphragm, said chain connecting the diaphragm with the brake and operative to cause the brake to function when pressure is admitted to the pressure chamber, said diaphragm having normally a relatively small amplitude of swing to actuate the brake when the chain is substantially free of slack and having a greater ampli-- tude of swing when there is slack in the chain, pneumatically powered mechanism operating on the chain to take up automatically any slack therein, and a control for regulating the trans mission of pneumatic power therethrough to said mechanism, said control including a control casing carried by the main casing as an attachment thereto, a spring-loaded plunger guided in the control casing and having its advance end located in the mechanism controlling chamber in position normally spaced from the diaphragm when on its normal and relatively small amplitude of swing and in position to be moved by the diaphragm when on its greater amplitude of swing, thereby to cause the pneumatically actuated mechanism to function.

ALBERT F. SHIELDS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS- Number Name Date 1,284,614 Desmond Nov. 12, 1918 1,604,267 Down Oct. 26, 1926 1,673,073 Kempton et al June 12, 1923 1,689,235 Fowler et al. Oct. 30, 1928 2,084,662 Williamson June 22, 1937 2,097,533 Redford Nov. 2, 1937 2,156,154 Hooker Apr. 25, 1939 2,246,201 Farmer June 17, 1941 2,379,796 Freeman et a1 July 3, 1945 FOREIGN PATENTS Number Country Date 650,826 Germany of 1936 

